In general, they report in the American Journal of Clinical
Nutrition, the studies were small, short-term and had substantial
differences in their methodology that make it hard to draw firm
conclusions.

One problem is that the trials included a wide range of
patients, according to Dr Katherine M. Appleton and her colleagues
at the University of Bristol. Some studies examined adults with
major depression, while others focused on bipolar disorder. Some
assessed depression in people with other disorders, such as chronic
fatigue syndrome or obsessive-compulsive disorder.

In addition, the treatment type and doses varied widely. In some
studies, participants took omega-3 supplements along with their
standard therapy, while other studies used only the supplements.
One study looked at the effects of eating fish.

"Trial evidence that examines the effects of omega-3 PUFAs on
depressed mood is limited and is difficult to summarise and
evaluate because of considerable heterogeneity," Appleton and her
colleagues write.

What evidence there is, they conclude, offers "little support"
for using fish oil to fight depression.

In theory, omega-3 fats could affect depression symptoms through
their action in the brain. Several studies have suggested the fatty
acids aid in the function of certain chemical messengers in the
brain that are linked to depression.

In addition, some population studies have found that people who
regularly eat fish have a relatively lower risk of depression.

However, the promise from studies like these is not always
duplicated in clinical trials, where researchers rigorously test a
treatment against a placebo, or inactive treatment.

According to Appleton's team, larger, well-conducted clinical
trials of fish oil for depression are still needed.